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19-2597; Rev 0; 10/02
3.2Gbps Compact SFP VCSEL Driver
General Description
The MAX3741 is a high-speed VCSEL driver for smallform-factor (SFF) and small-form-factor pluggable (SFP) fiber-optic LAN transmitters. It contains a bias generator, laser modulator, and peaking current option to improve VCSEL edge speed. The driver accommodates common cathode and differential configurations. The MAX3741 operates up to 3.2Gbps. It can switch up to 15mA of laser modulation current and source up to 15mA of bias current. The MAX3741 is designed to interface with a digital potentiometer and control circuitry. The MAX3741 accommodates various VCSEL packages, including low-cost TO-46 headers. The MAX3741 is available in a compact 3mm x 3mm 16-pin thin QFN package and operates over a temperature range of -40C to +85C. o 2mA to 15mA Modulation Current o 1mA to 15mA Bias Current o Optional Peaking Current to Improve VCSEL Edge Speed o Supports Common Cathode and Differential Configuration o 3mm x 3mm 16-Pin Thin QFN Package
Features
MAX3741
Applications
Multirate (1Gbps to 3.2Gbps) SFP/SFF Modules Gigabit Ethernet Optical Transmitters Fibre Channel Optical Transmitters
PART MAX3741ETE
Ordering Information
TEMP RANGE -40C to +85C PIN-PACKAGE 16 Thin QFN-EP*
*EP = exposed pad.
Typical Application Circuit
+3.3V
Pin Configuration
VCC BIAS 0.1F IN+ IN0.1F MAX3741 OUT+ 0.01F OUT50 TX_DISABLE BIASSET MODSET BIASMON GND PEAKSET RPEAKSET 0.01F L1*
16
15
14
13
TX_DISABLE IN+ INN.C.
BIAS 12 BIASMON 11 OUT+ 10 OUT9
GND
1 2 3 4 5 VCC 6 7 PEAKSET 8
MAX3741 3mm x 3mm
VCC
TOP VIEW
BIASSET
0.01F
VCC
MODSET
RBIASSET
RMODSET
RMON
THIN QFN
EXPOSED PAD IS CONNECTED TO GND.
THIS SYMBOL REPRESENTS A TRANSMISSION LINE OF CHARACTERISTIC IMPEDANCE Zo = 50. * FERRITE BEAD, MURATA BLM18HD102SN1B
________________________________________________________________ Maxim Integrated Products
GND
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
3.2Gbps Compact SFP VCSEL Driver MAX3741
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC) ............................................-0.5V to +5.0V Voltage at TX_DISABLE, IN+, IN-, MODSET, PEAKSET, BIASSET, BIAS, BIASMON .......-0.5V to (VCC + 0.5V) Voltage at OUT+, OUT- .........................(VCC - 2V) to (VCC + 2V) Current into OUT+, OUT- ....................................................60mA Continuous Power Dissipation (TA = +85C) 16-Lead Thin QFN (derate 25mW/C above +85C) ..........2W Operating Temperature Range .......................... -40C to +85C Storage Temperature Range .............................-55C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +2.97V to +3.63V, TA = -40C to +85C. Typical values are at VCC = +3.3V, TA = +25C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS TX_DISABLE set low, peaking is not used (Note 1) IMOD = 2mAP-P IMOD = 15mAP-P MIN TYP 41 51 14 0.15 80 VIH VIL t_off TX_DISABLE Time t_on Input Leakage BIAS GENERATOR (Note 4) Bias Current Accuracy of Programmed Bias Current Bias Current During Disable BIASMON Gain LASER MODULATOR (Note 5) Data Input Voltage Swing Output Resistance Modulation Current VID ROUT IMOD Total differential signal Single-ended resistance at OUT+, OUTMin Max 15 250 63 2200 80 2 mVP-P mAP-P IBIAS IBIAS IBIAS_OFF TX_DISABLE high 0.095 0.115 Min Max 15 -8 +8 10 0.135 1 mA % A mA/mA Time from rising edge of TX_DISABLE to IBIAS = IBIAS_OFF and IMOD = IMOD_OFF (Note 3) Time from falling edge of TX_DISABLE to IBIAS = 15mA and IMOD = 15mAP-P VCC = 0V and VTX_DISABLE = 3.3V 0.2 2 0.8 3 s 111 25 40 A 105 65 mA 20 1 k V V MAX UNITS
Supply Current
ICC
Additional current when peaking is used (Note 2) ICC-SHDW Total current when TX_DISABLE is high
TX_DISABLE INPUT Input Impedance Input High Voltage Input Low Voltage
2
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3.2Gbps Compact SFP VCSEL Driver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.97V to +3.63V, TA = -40C to +85C. Typical values are at VCC = +3.3V, TA = +25C, unless otherwise noted.)
PARAMETER Programmable Peaking Current Peaking Current Duration Tolerance of Programmed Modulation Current Modulation Transition Time Deterministic Jitter Random Jitter Laser Modulation During Disable Differential Input Resistance Input Bias Voltage VIN t R , tF DJ RJ IMOD_OFF 5mAP-P IMOD 15mAP-P (Note 3) 5mAP-P IMOD 15mAP-P (Notes 3, 6) (Note 3) Differential input voltage at 2200mVP-P 85 -10 65 13 1 15 100 VCC 0.3 SYMBOL IPEAK Min Max CONDITIONS MIN TYP 0.2 2 80 +10 95 25 4 50 115 MAX UNITS mA ps % ps psP-P psRMS AP-P V
MAX3741
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6:
Measured with RBIASSET = 1.87k (IBIAS 15mA). Supply current excludes IBIAS. Tested with RPEAK = 1.18k. Guaranteed by design and characterization. VBIAS is less than VCC - 0.7V. Measured electrically with a 50 load AC-coupled to OUT+. Deterministic jitter is the peak-to-peak deviation from the ideal time crossings measured with a K28.5 bit pattern at 3.2Gbps (00111110101100000101).
Typical Operating Characteristics
(VCC = +3.3V, TA = 25C, measured electrically with a 50 load AC-coupled to OUT+, unless otherwise noted.)
ELECTRICAL EYE
MAX3741 toc01
ELECTRICAL EYE WITH PEAKING
MAX3741 toc02
ELECTRICAL EYE WITH PEAKING
MAX3741 toc03
3.2Gbps, K28.5, 10mA MODULATION, NO PEAKING
3.2Gbps, K28.5, 10mA MODULATION, RPEAKSET = 2.4k
3.2Gbps, K28.5, 10mA MODULATION, RPEAKSET = 500
87mV/div
87mV/div
87mV/div
50ps/div
50ps/div
50ps/div
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3
3.2Gbps Compact SFP VCSEL Driver MAX3741
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = 25C, measured electrically with a 50 load AC-coupled to OUT+, unless otherwise noted.)
OPTICAL EYE AT 2.125Gbps
MAX3741 toc04
OPTICAL EYE
MAX3741 toc05
DETERMINISTIC JITTER vs. IMOD
24 20 16 12 8 4 0
MAX3741 toc06
(ER = 8.8dB, K28.5, 850nm VCSEL, WITH 2.3GHz O-TO-E CONVERTER)
(ER = 8.8dB, 1.063Gbps, K28.5, 850nm VCSEL, WITH 2.3GHz O-TO-E CONVERTER)
28
68ps/div
135ps/div
DETERMINISTIC JITTER (psP-P)
0
5
10
15
MODULATION CURRENT (mAP-P)
RANDOM JITTER vs. IMOD
MAX3741 toc07
BIAS CURRENT vs. RBIASSET
MAX3741 toc08
IMOD vs. RMODSET
14 12 10 8 6 4 2 0
MAX3741 toc09
4.0 3.5 RANDOM JITTER (psRMS) 3.0 2.5 2.0 1.5 1.0 0.5 0 0 5 10
16 14 BIAS CURRENT (mA) 12 10 8 6 4 2 0 0 5 10 15 RBIASSET (k) 20 25
16 MODULATION CURRENT (mAP-P)
15
30
0
2
4
6 RMODSET (k)
8
10
12
MODULATION CURRENT (mAP-P)
IBIASMON vs. BIAS CURRENT
MAX3741 toc10
INPUT RETURN LOSS
MAX3741 toc11
OUTPUT RETURN LOSS
-2 -4 -6 S22 (dB) -8 -10 -12 -14 -16
MAX3741 toc12
1.8 1.6 1.4 IBIASMON (mA) 1.2
0 -5 -10 S11 (dB) -15 -20 -25 -30 -35 100M DIFFERENTIAL MEASUREMENT
0
1.0 0.8 0.6 0.4 0.2 0 0 4 8 BIAS CURRENT (mA) 12 16
-18 1G FREQUENCY (Hz) 10G -20 100M 1G FREQUENCY (Hz) 10G
4
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3.2Gbps Compact SFP VCSEL Driver
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = 25C, measured electrically with a 50 load AC-coupled to OUT+, unless otherwise noted.)
MAX3741
TRANSITION TIME vs. IMOD
MAX3741 toc13
SUPPLY CURRENT vs. TEMPERATURE
MAX3741 toc14
POWER-SUPPLY REJECTION
PSR = 20log VOUT VCC
MAX3741 toc15
80 75 TRANSITION TIME (ps) 70 65 60 55 50 45 40 2 4 6 8 10 12 14 FALL TIME RISE TIME MEASURED FROM 20% TO 80%
80 70 SUPPLY CURRENT (mA) 60 50 40 30 20 10
IMOD = 2mAP-P
0 -2 -4 PSR (dB) -6 -8 -10 -12
16
-40
-15
10
35
60
85
100
1k
10k
100k
1M
10M
100M
IMOD (mA)
TEMPERATURE (C)
FREQUENCY (Hz)
Pin Description
PIN 1 2 3 4 5, 9, 15 6 7 8, 16 10 11 12 13 14 EP NAME TX_DISABLE IN+ INN.C. VCC MODSET PEAKSET GND OUTOUT+ BIASMON BIAS BIASSET Exposed Pad FUNCTION Transmit Disable. Driver output is disabled when TX_DISABLE is high or left unconnected. The driver output is enabled when the pin is asserted low. Noninverted Data Input Inverted Data Input No Connection +3.3V Supply Voltage Modulation Set. A resistor connected from MODSET to ground (RMODSET) programs the desired modulation current amplitude. Peaking Current Set. A resistor connected between PEAKSET and ground (RPEAKSET) programs the peaking current amplitude. To disable peaking, leave PEAKSET open. Ground Inverted Modulation-Current Output Noninverted Modulation-Current Output Bias Current Monitor. The output of BIASMON is a sourced current proportional to the bias current. A resistor connected between BIASMON and ground (RBIASMON) can be used to form a ground referenced bias monitor. Bias Current Output Bias Current Set. A resistor connected between BIASSET and ground (RBIASSET) programs the VCSEL bias current. Ground. This must be soldered to the circuit board ground for proper thermal and electrical performance. See the Layout Considerations section.
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5
3.2Gbps Compact SFP VCSEL Driver MAX3741
Functional Diagram
BIASSET ENABLE BIASMON
Input Termination
The MAX3741 data inputs are SFP MSA compatible. On-chip 100 differential input impedance is provided for optimal termination (Figure 4). The MAX3741 inputs self-bias to the proper operating point to accommodate AC-coupling.
TX_DISABLE
BIAS GENERATOR VCC
BIAS
Applications Information
VCSEL Selection
Select a communications-grade VCSEL with a rise time of 260ps or better for 1.25Gbps or 130ps or better for 2.5Gbps applications. Use a high-efficiency VCSEL that requires low modulation current and generates a low voltage swing. Trim the leads to reduce VCSEL package inductance. The typical package leads have inductance of 25nH per inch (1nH/mm). This inductance causes a large voltage swing across the VCSEL. A compensation filter network can be used to reduce ringing, edge speed, and voltage swing. See the Designing the Laser-Compensation Filter Network section for more information.
LASER MODULATOR ROUT OUTOUT+
MAX3741 ROUT
IN+ 100 INENABLE MODULATION-CURRENT GENERATOR PEAKING CONTROL
MODSET
PEAKSET
Layout Considerations
Detailed Description
The MAX3741 contains a bias generator and a laser modulator with optional peaking compensation.
To minimize inductance, keep the connections between the MAX3741 output pins and VCSEL as close as possible. Use good high-frequency layout techniques and multiple-layer boards with uninterrupted ground planes to minimize EMI and crosstalk.
Bias Generator
Figure 1 shows the bias generator circuitry that contains a bandgap voltage reference, current mirror, and bias monitor. The bias current output to the laser is controlled with the RBIASSET resistor. For appropriate RBIASSET values, see the Bias Current vs. RBIASSET graph in the Typical Operating Characteristics. The BIASMON output provides a current proportional to the laser bias current given by: IBIASMON = IBIAS / 9
CURRENT AMPLIFIER MAX3741 IBIAS 40 ENABLE BIAS
BIASMON 0.8V IBIAS 9
FERRITE BEAD
Modulation Circuit
The modulation circuitry consists of an input buffer, a current mirror, and a high-speed current switch (Figure 2). The modulators drive up to 15mA of modulation into a 50 VCSEL load. The amplitude of the modulation current is set with resistor at MODSET (RMODSET). For appropriate RMODSET values, see the IMOD vs. RMODSET graph in the Typical Operating Characteristics. Figure 3 shows a simplified diagram of the MAX3741 output stage.
200 BIAS GENERATOR BIASSET RBIASSET RBIASMON
Figure 1. Bias Generator
6
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3.2Gbps Compact SFP VCSEL Driver
Designing the Compensation Filter Network
ROUT OUT+ OUTPEAKING CONTROL PEAKSET MODULATION CURRENT GENERATION
MAX3741
VCC
MAX3741
ROUT CURRENT SWITCH
IN+ 100 IN-
INPUT BUFFER
VCSEL package inductance causes the VCSEL impedance to increase at high frequencies, leading to ringing, overshoot, and degradation of the VCSEL output. A VCSEL compensation filter network can be used to reduce the VCSEL impedance at high frequencies, thereby reducing output ringing and overshoot. The compensation components (RF and CF) are most easily determined by experimentation. Begin with RF = 50 and CF = 1pF. Increase CF until the desired transmitter response is obtained (Figure 5). Refer to Application Note HFAN-2.0: Interfacing Maxim Laser Drivers with Laser Diodes for more information.
CURRENT AMPLIFIER 34x
RPEAKSET
ENABLE
Exposed-Pad (EP) Package
The exposed pad on the 16-pin thin QFN provides a very low thermal resistance path for heat removal from the IC. The pad is electrical ground on the MAX3741 and must be soldered to the circuit board ground for proper thermal and electrical performance. Refer to Maxim Application Note HFAN-08.1: Thermal Considerations for QFN and Other Exposed Pad Packages, for additional information.
1.0V
MODSET RMODSET
Figure 2. Modulation Circuit
VCC MAX3741 ROUT PACKAGE ROUT 1nH 0.5pF IN+ 1nH 0.5pF VCC 50 IN1nH 0.5pF MAX3741 24k OUT+ 1nH 0.5pF 50 OUTPACKAGE 16k VCC VCC
Figure 3. Simplified Output Structure
Figure 4. Simplified Input Structure
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7
3.2Gbps Compact SFP VCSEL Driver MAX3741
Laser Safety and IEC 825
The International Electrotechnical Commission (IEC) determines standards for hazardous light emissions from fiber-optic transmitters. IEC 825 defines the maximum light output for various hazard levels. Using this laser driver alone does not ensure that a transmitter design is compliant with IEC 825. The entire transmitter circuit and component selections must be considered. Customers must determine the level of fault tolerance required by their applications, recognizing that Maxim products are not designed or authorized for use as components in systems intended for surgical implant into the body, for applications intended to support or sustain life, or for any other application where the failure of a Maxim product could create a situation where personal injury or death may occur.
UNCOMPENSATED
CORRECTLY COMPENSATED POWER
OVERCOMPENSATED
TIME
Figure 5. Laser Compensation
Chip Information
TRANSISTOR COUNT: 1597 PROCESS: SiGe bipolar
Package Information
For the latest package outline information, go to www.maxim-ic.com/packages.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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